Vehicle engines produce oxides of nitrogen (NOx) as a component of vehicle emissions. In an effort to reduce NOx levels in vehicle emissions, manufacturers typically employ an exhaust gas recirculation (EGR) system. The EGR system reduces NOx levels by recirculating exhaust gas into the intake manifold where the exhaust gas mixes with incoming air and fuel. NOx forms in high concentrations when combustion temperatures exceed a predetermined temperature. By diluting the air/fuel ratio, peak combustion temperatures are reduced.
Combustion temperatures can be further reduced by cooling the re-circulated exhaust gas. Therefore, some EGR systems include a heat exchanger that cools the exhaust gas before injection into the intake manifold. A valve or other metering device may be used to regulate the flow of exhaust into the intake manifold.
In the heat exchanger, the exhaust travels through a plurality of heat exchange conduits that are made from a thermally conductive material. One surface of the heat exchange conduits is in contact with the exhaust gas and another surface is in contact with a fluid (coolant or air) that absorbs heat from the exhaust gas. The heat transfer efficiency may be reduced due to fouling or coagulation of exhaust particles in the heat exchange conduits. As a result, the heat exchanger is usually oversized to compensate for fouling. This compromises packaging space, heat exchanger design, and/or vehicle weight.